1. Field of the Invention
The present invention relates to a method for setting a path between a gateway and a node that are structuring an ad-hoc network, and more particularly, to a method for setting a path for sending data from the node to the gateway.
2. Description of Related Art
General mobile communication systems transmit and receive data between a mobile element and a base station. The mobile terminal and the base station directly transmit and receive data without passing through other mobile terminals and nodes. However, the ad-hoc network uses other nodes in transmitting data of a specific node to a gateway (GW).
Hereinafter, description will be made on a structure of the ad-hoc network with reference to FIG. 1. As shown in FIG. 1, the ad-hoc network has a gateway and plural nodes. In FIG. 1, the nodes are represented by circles. FIG. 1 shows only one gateway, but the ad-hoc network can have at least two gateways according to user's setting.
The gateway transmits to a different communication system such as the Internet network data transmitted by nodes constructing the ad-hoc network. The plural nodes transmit data to the gateway. The nodes, which are located within a certain distance from the gateway, directly transmit data to the gateway. However, nodes which are located beyond the certain distance transmit collected data to nodes neighboring the gateway instead of directly transmitting the data to the gateway. That is, the nodes beyond the certain distance transmit data by using neighboring nodes, which minimizes power consumption for data transmissions. And, the distance between a gateway and a node is proportional to the power consumption for the node to transmit specific data. Thus, the nodes beyond a certain distance from the gateway transmit the collected data by use of plural nodes, so the power consumption can be minimized during data transmission. Hereinafter, nodes which relay data of other nodes are called “relay nodes.” The relay nodes transmit data which they collect, directly or through different relay nodes, to the gateway.
Hereinafter, description will be made on a process for setting a path through which nodes constructing an ad-hoc network transmit data to a gateway. The path for data transmissions is established through the following four steps:                Gateway Solicitation Process        Gateway Advertisement Process        Process for generating a Global Address for Internet        Sending Data        
Hereinafter, description will be made of the above four steps for setting a path for data transmissions with reference to FIG. 2. The Gateway Solicitation Process (S200) is a process for a node entered in an ad-hoc network to solicit a gateway location. The node can transmit data to the gateway only when the node knows where the gateway is located. Thus, the node broadcasts a message including information on its own address and information requesting a gateway address. Neighboring nodes having received the message decide whether to be the gateway requested by the node. In general, the gateway is aware that it is a gateway. Therefore, the neighboring nodes that have received the message update and transmit the received message to different neighboring nodes. That is, the neighboring nodes take out of the received message and store the information of the addresses of the nodes sending the message, and send a message having their own address information. The above process is carried out until the message sent by the node is delivered to the gateway. The gateway can recognize that the node solicits a response, using the information included in the sent message. The message the node has sent is transmitted to at least one gateway constructing the ad-hoc network.
The network that has carried out the Gateway Solicitation Process performs the Gateway Advertisement Process (S202). The Gateway Advertisement Process is a process by which the gateway which finally received the message the note had sent transmits its own address information to the node. The gateway extracts the address information of the node included in the message received in the Gateway Solicitation Process. The gateway transmits a message including its own address information to the node having the extracted address information. Unlike the Gateway Solicitation Process, the message received and sent in the Gateway Advertisement Process is unicast. That is, the message the gateway has sent can be unicast to the node by use of the address information obtained in the Gateway Solicitation Process. Further, the nodes that received the message the gateway had sent count the number of hops. That is, the nodes add one to the number of hops included in the message received from a previous node, and send the number of hops added by one to a next node. The process as above enables the node requesting the location information of the gateway to obtain the location information of the gateway and the number of hops up to the gateway. And, if plural gateways exist, the node can obtain the information of the individual gateways.
The process for generating a Global Address for Internet (S204) is a process for the node to generate his unique address by use of its obtained information. If a gateway is picked up for data to be sent, the node sends data by use of an established path (S206).
However, it takes a long time to send data through the above-described processes for data transmission. Thus, there is a need for a method which reduces the time required to send data from a node included in the ac-hoc network to a gateway.